Billboards - placing text on the screen.

Ok, so this is going to be a bit long but I have been pulling my hair out over this for weeks. I am trying to place text on the screen using 1 quad (2xtris) for each letter and then referencing a texture map for the character. I have billboarding working as far as the text always facing the camera but I cannot seem to get it to always draw in a particular part of the screen. My camera view looks both up/down and side to side. I have it so that it will draw in the same place when I move the camera front and back and side to side or when I rotate it on the Y axis but for some reason I can't nail down how to keep the text locked into the screen when I look "up and down." I can manipulate the code such that Y axis rotations work OR x-z axes work but not both simultaneously. Code is in Euphoria but similar enough to C that it should be understandable:

It is probably easiest to switch to an orthographic projection and use that to draw the text on top of your scene (with depth testing disabled), just make sure you render it after everything else.

Thanks for the info Carsten. Does anyone know of a good place on how to do that using modern opengl? I have been poking around all morning and it seems like everything is using fixed function or a bit vague.